Sexual Rejection Increases Aggression and Stress in Male Fruit Flies

Summary: A new study reveals how fruit flies respond to the stress of repeated mating failures. Researchers observed that male fruit flies facing repeated sexual rejection showed increased activity, aggression, and anti-social behavior, indicating a frustration-like stress state. This stress response was linked to the neuropeptide F signaling system in the brain, which is crucial for reward processing and aggression.

The study demonstrates for the first time that social stress in fruit flies, caused by mating failures, affects their resilience to other stressors like starvation and toxic exposure. This research provides valuable insights into the neurobiological basis of social stress in a model organism.

Key Facts:

  1. Repeated mating failures in fruit flies lead to increased activity, aggression, and social withdrawal.
  2. The stress response is mediated by the neuropeptide F signaling system in the brain.
  3. This study opens new avenues for researching social stress in simpler organisms.

Source: PLOS

Repeated failures to reproduce make fruit flies stressed and frustrated, which in turn makes them less resilient to other types of stress. Julia Ryvkin at Bar-Ilan University and colleagues report in the open-access journal PLOS Genetics, published January 18.

Animals are motivated to take actions that improve their survival and reproduction through reward systems in the brain, but failure causes stress. The reward systems have been extensively studied, but less attention has been paid to how animals respond to failure.

This shows a fruitfly.
These results show for the first time that fruit flies experience social stress when their attempts to mate repeatedly fail. Credit: Neuroscience News

To investigate, researchers compared the behaviour of male fruit flies (Drosophila melanogaster) that had experienced repeated sexual rejection, with males that had recently mated and naïve males that had been kept in isolation.

They found that rejected males were more active, more aggressive, and less social towards other males — indicating a frustration-like state of stress.

Rejected males were also less resilient to two other types of stress: starvation and exposure to a toxic herbicide that causes oxidative damage.

To understand how this stress response is controlled in the brain, the researchers manipulated the signaling system of neuropeptide F, which is involved in reward processing and aggression.

Inhibiting neuropeptide F receptors made flies less resilient against starvation, mimicking the effects of repeated sexual rejection.

Using a technique called optogenetics, which uses light to stimulate activity in specific cells, the team activated neuropeptide F receptor neurons and found that this also reduced the flies’ ability to withstand starvation.

These results show for the first time that fruit flies experience social stress when their attempts to mate repeatedly fail. The response is mediated by a brain signaling system involving neuropeptide F, which also plays a role in reward- and stress-responses in other organisms.

This offers an opportunity to further investigate social stress in a model organism with a simple nervous system, the authors say.

Funding: This work was supported by the Israel Science Foundation Grants (384/14 and 174/19 to GSO). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

About this neuroscience and psychology research news

Author: Charlotte Bhaskar
Source: PLOS
Contact: Charlotte Bhaskar – PLOS
Image: The image is credited to Neuroscience News

Original Research: Open access.
Failure to mate enhances investment in behaviors that may promote mating reward and impairs the ability to cope with stressors via a subpopulation of Neuropeptide F receptor neurons” by Ryvkin J et al. PLOS Genetics


Failure to mate enhances investment in behaviors that may promote mating reward and impairs the ability to cope with stressors via a subpopulation of Neuropeptide F receptor neurons

Living in dynamic environments such as the social domain, where interaction with others determines the reproductive success of individuals, requires the ability to recognize opportunities to obtain natural rewards and cope with challenges that are associated with achieving them.

As such, actions that promote survival and reproduction are reinforced by the brain reward system, whereas coping with the challenges associated with obtaining these rewards is mediated by stress-response pathways, the activation of which can impair health and shorten lifespan.

While much research has been devoted to understanding mechanisms underlying the way by which natural rewards are processed by the reward system, less attention has been given to the consequences of failure to obtain a desirable reward.

As a model system to study the impact of failure to obtain a natural reward, we used the well-established courtship suppression paradigm in Drosophila melanogaster as means to induce repeated failures to obtain sexual reward in male flies.

We discovered that beyond the known reduction in courtship actions caused by interaction with non-receptive females, repeated failures to mate induce a stress response characterized by persistent motivation to obtain the sexual reward, reduced male-male social interaction, and enhanced aggression.

This frustrative-like state caused by the conflict between high motivation to obtain sexual reward and the inability to fulfill their mating drive impairs the capacity of rejected males to tolerate stressors such as starvation and oxidative stress.

We further show that sensitivity to starvation and enhanced social arousal is mediated by the disinhibition of a small population of neurons that express receptors for the fly homologue of neuropeptide Y.

Our findings demonstrate for the first time the existence of social stress in flies and offers a framework to study mechanisms underlying the crosstalk between reward, stress, and reproduction in a simple nervous system that is highly amenable to genetic manipulation.

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